I have meet a problem in ospf, i have two sites with 2 routers running ospf, configuration is basic, 2 router connect each other over 1 tunnel GRE. In normal, ospf is running well, but when i "shutdown" tunnel of 2 router and "no shut" it active again, but ospf is not running again, i troubleshoot and i see:
"Oct 26 01:33:52.362: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.2.1 on Tunnel15 from DOWN to DOWN, Neighbor Down: Ignore timer expired
:12.338: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.2.1 on Tunnel15 from EXCHANGE to DOWN, Neighbor Down: Too many retransmissions" . OSPF process is reaching Exchange state but it is not Fullloading. I wonder why ??
So, Everone know that is, or have the same erro, could help me
This is typical problem for "exchange" state of the OSPF neighbor relation ship. And answer to adjust MTU size is correct in my opinion. The thing is you need to specify it on GRE interface as well as physical interface on wihch GRE is terminating. ( on both side routers )
Try setting it to 1450. ( not 1500 ).
Clear ospf process and see if still it is getting sturck in "exchange" phase.